Semiconductor devices are used in many types of products. Typically, semiconductor devices are manufactured by first growing generally cylindrical-shaped silicon (or other base semiconductive material) ingots. The ingots may then be sliced into generally flat, circular wafers; Through a variety of thermal, chemical, and physical processes, including diffusion, oxidation, epitaxial growth, ion implantation, deposition, etching, sputtering, polishing, and cleaning, active and passive devices may be formed on one or both surfaces of the wafer. The wafer may then be cut into individual rectangular semiconductor die, which may then be attached to a leadframe, encapsulated, and packaged as a discrete or integrated circuit. The packaged discrete and integrated circuits may be mounted to printed circuit boards and interconnected to perform the desired electrical function.
More recently, another type of semiconductor integrated circuit device, known as a spherical shaped integrated circuit, has emerged. Spherical shaped integrated circuits provide various advantages over conventional flat integrated circuits. For example, the physical dimensions of spherical integrated circuit allow it to adapt to many different manufacturing processes. Moreover, due to its shape, spherical shaped integrated circuits shape have greater surface area as compared to conventional integrated circuits. Hence, a spherical integrated circuit may have more (or larger) circuits and circuit elements formed on its surface, as compared to a conventional, flat integrated circuit. A spherical shaped integrated circuit may be manufactured by using a variety of conventional thermal, chemical, and physical processing steps.
A system and method for manufacturing spherical shaped integrated circuits is disclosed in U.S. Pat. No. 5,955,776 (“Ishikawa”). In accordance with Ishikawa, once the spherical semiconductor crystals are formed, each undergoes a variety of conventional thermal, chemical, and physical processes. Thereafter, the circuit elements are formed in the spherical surface using the same basic processing steps that are used to form circuit elements on conventional, flat integrated circuits. In particular, a photoresist is applied to the surface of the sphere. Then, using an exposure apparatus, light from a light source is irradiated through a mask onto the spherical surface. The mask has a circuit pattern formed on it and, as a result, this circuit pattern is projected onto the surface of the spherical shaped semiconductor. The masked light reacts with the photoresist to form the desired circuit on the surface of the sphere.
To ensure that the circuit pattern is projected on the surface of the spherical shaped semiconductor with sufficient precision, the center of the spherical shaped semiconductor should coincide with the optical axis of the exposure apparatus before exposing the surface to the masked light. One method of providing proper alignment is to form alignment marks on the surface of the spherical shaped semiconductor. These alignment marks are used to detect and correct any position deviations, and properly position the spherical shaped semiconductor on a support stand. The support stand is then moved to the appropriate position in the exposure apparatus, such that the optical axis of the exposure apparatus coincides with the center of the spherical-shaped semiconductor.
Although the above-described positioning process generally works well, it does exhibit certain drawbacks. In particular, if the position of the alignment marks is sensed using an optical sensing device, it may not be possible to detect position deviations with a sufficiently high degree of sensitivity. This can be seen by referring to FIGS. 8 and 9. As FIG. 8 illustrates, when the alignment mark 802 on the surface of the spherical shaped semiconductor 804 coincides with the optical axis 806 of an optical system such as, for example, an exposure apparatus, the width of the alignment mark 802 is seen as being W0 by an optical sensing device. Conversely, as FIG. 9 illustrates, a slight counterclockwise rotation of the spherical shaped semiconductor 804 causes a deviation (dy). If the spherical shaped semiconductor 804 is then rotated clockwise so that the width of the alignment mark is seen as W0, then the deviation (dy) will still exist between the center of the alignment mark and the optical axis 806. Thus, the spherical shaped semiconductor 804 may be translated until the center of the alignment mark coincides with the optical axis 806, and the width of the alignment mark is seen as being W1. For example, as illustrated in FIG. 9, when an incremental position deviation (“dy”) between the optical axis 806 of the optical system and the center of the spherical-shaped semiconductor is present, the distance from the principle plane of an object lens, represented in FIGS. 8 and 9 as a plane P1, to the surface of the spherical shaped semiconductor 804 becomes Z0+dz1 at one point, and Z0−dz2 at another point, compared to the proper distance of Z0. During exposure, such a difference of distance can cause the image of the circuit pattern projected onto the surface of the spherical shaped semiconductor to become unclear.
Another problem associated with the above-described positioning process is that it is not possible to correction any detected position deviation once the spherical shaped semiconductor is mounted on the support stand and positioned in the exposure apparatus. That is, after the spherical shaped semiconductor is placed on the support stand and it is positioned within the exposure apparatus, there is a possibility that a position deviation may subsequently occur. The size of this position deviation depends, at least in part, on the precision of the construction of the mechanism that moves the support stand, making it extremely difficult to complete eliminate this possible movement.
Hence, there is a need for a system and method that detects and/or corrects position deviations between the optical axis of an optical system, such as an exposure apparatus, and the center of a spherical shaped object, such as a spherical shaped semiconductor, that does not rely on an alignment mark formed on the surface of the object. There is additionally a need for a system and method that detects and/or corrects position deviations between the optical axis of an optical system and the center of a spherical shaped object after the object is positioned within an exposure apparatus. The present invention addresses one or more of these needs.